thmjpr

Come on man, that is a poor argument. Its more likely you'd mis-hear the value than the units. Get some post it notes and a pen next time.
It should be obvious why powers of 10 on scope scaling is not used, it is a visual instrument. Thankfully the units themselves (volts) are metric.
http://metric4us.com/

Good point, just friction then. Push or tilt the bolt to increase.
I tried to find dimensions for DIN603 M3 carriage bolt, couldn't find any specifics but it doesn't seem like it would work. Could also use a T bolt which would have a rectangular head.
Presumably it was a cost/availability decision to use the simpler style bolt.

Backlight off doesn't seem to work (at least with the source code zip provided).
backlight_counter is being incremented and then checked if its equal to brightness_setting, which will never occur if brightness is 0. So off is the same as 100%.
Although I suspect the intention was to disable the timer interrupt if brightness_setting = 0?

ATxmega includes an internal 32.768kHz oscillator accurate to +/- 0.5%, and a 2 or 32MHz accurate to +/- 1.5%. This is suitable for serial communication.
You could add that external crystal if you want higher accuracy for something like timekeeping.

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